Romanos Lekapenos had risen to power in 919, when he had managed to appoint himself
regent over the young Constantine VII and marry his daughter Helena to him. Within a year, he successively rose from
basileopator to
caesar, and was eventually crowned senior emperor on 17 December 920. To consolidate his hold on power, and with a view of supplanting the ruling
Macedonian dynasty with his own family, he raised his eldest son Christopher to co-emperor in May 921, while Stephen and Constantine were proclaimed co-emperors on 25 December 924. Following Christopher's early death in 931, and given Constantine VII's
de facto sidelining, Stephen and Constantine assumed an increased prominence, although formally they still ranked after their brother-in-law in the college of emperors. In 933, Stephen was married to Anna, the daughter of a certain Gabalas, who was crowned
Augusta on the same occasion. The couple had one known son, Romanos. According to the 11th-century chronicler
George Kedrenos, he was
castrated in 945, but later became a
sebastophoros. Predictably, Stephen and Constantine opposed this decision, and prevailed upon their father, who was by this time ill and old, to dismiss Kourkouas in the autumn of 944. Romanos II instead married
Bertha, an illegitimate daughter of King
Hugh of Italy, who changed her name to Eudokia after her marriage. Their fellow conspirators included
Marianos Argyros, the
protospatharios Basil Peteinos,
Manuel Kourtikes, the
strategos Diogenes, Clado, and Philip. Kedrenos, however, considers Peteinos to have served as an agent of Constantine VII among the conspirators. On 16 or 20 December 944, the conspirators set their plans in motion. The two brothers smuggled their supporters into the
Great Palace of Constantinople during the midday break in palace activities. They then led their men into the chamber of Romanos I, where they easily captured the "ill old man". They were able to transport him to the nearest harbour and from there to
Prote, one of the
Princes' Islands and a popular place of exile. There, Romanos agreed to take monastic vows and retire from the throne. Having managed to quietly depose their father, the brothers now had to deal with Constantine VII. Unfortunately for them, rumours soon spread around
Constantinople to the effect that, following Romanos's deposition, Constantine VII's life was in danger. Before long, crowds gathered before the palace, demanding to see their emperor in person. The contemporary
Lombard historian
Liutprand of Cremona notes that the ambassadors and envoys from
Amalfi,
Gaeta,
Rome, and
Provence present in the capital also supported Constantine VII. Stephen and his brother had to succumb to the inevitable, recognizing their brother-in-law as the senior emperor. The new triumvirate lasted for about 40 days. The three emperors soon appointed new leaders for the military services.
Bardas Phokas the Elder was appointed as the new
Domestic of the Schools, and
Constantine Gongyles as head of the
Byzantine navy. Stephen and his brother managed to reward their fellow conspirators. Peteinos became
patrikios and
Great Hetaeriarch, Argyros was appointed
Count of the Stable, Kourtikes a
patrikios and
droungarios of the Watch. On 27 January 945, ==Exile==